FIG. 13 shows, as an example of a conventional rotation detecting apparatus, a rotation detecting apparatus having the similar structure to a rotation detecting apparatus shown in FIG. 1 of Japanese Patent Laid-Open Publication No. 2013-44606 (Patent Document 1).
(Conventional Rotation Detecting Apparatus)
In FIG. 13, a rotation detecting apparatus 300 is an apparatus, for instance, which can detect a rotation direction and a rotation amount of a rotation shaft 301 of a servomotor provided in a movable portion of an industrial robot. The rotation detecting apparatus 300 comprises a movable section 302 fixed to the rotation shaft 301 and rotating according to rotation of the rotation shaft 301. A rotation direction and a rotation amount of the movable section 302 coincide with the rotation direction and the rotation amount of the rotation shaft 301.
In the movable section 302, four magnets 311, 312, 313 and 314 are provided. The magnets 311, 312, 313 and 314 are located in this order at intervals of 90 degrees in a leftward direction in a circumference direction of the movable section 302. In addition, the magnets 311 and 313 are located in such a way that N-poles are on their front sides, and the magnets 312 and 314 are located in such a way that S-poles are on their front side. According to this, magnetic fields whose directions change for every 90 degrees are generated at an outer circumference side of the movable section 302.
Moreover, in the vicinity of the movable section 302, three magnetic sensors 321, 322 and 323 are provided. Each of the magnetic sensors 321, 322 and 323 is formed by winding a coil around a composite magnetic wire, which is a magnetic element producing large Barkhausen effect. The magnetic sensors 321, 322 and 323 are located in this order in a rightward direction so as to be along a circular external shape of the movable section 302 and the interval of the magnetic sensors adjacent to each other is 30 degrees.
The magnets 311, 312, 313 and 314 are fixed to the movable section 302 and changes their positions according to rotation of the movable section 302, whereas the magnetic sensors 321, 322 and 323 are fixed to a not-shown supporting section or the like and are unmovable.
When the magnet 311 approaches the magnetic sensor 321 by the rotation of the movable section 302, a magnetization direction of the magnetic sensor 321 is inverted by the magnetic field generated by the magnet 311. By electromotive force generated at this time, a detection pulse (hereinafter, this is called as “positive directional detection pulse”) whose level stands up in a positive direction is outputted from the magnetic sensor 321. The same goes for the time when the magnet 313 approaches the magnetic sensor 321. Also, the same goes for the magnetic sensors 322 and 323.
On the other hand, when the magnet 312 approaches the magnetic sensor 321 by the rotation of the movable section 302, the magnetization direction of the magnetic sensor 321 is inverted by the magnetic field generated by the magnet 312. By electromotive force generated at this time, a detection pulse (hereinafter, this is called as “negative directional detection pulse”) whose level stands up in a negative direction is outputted from the magnetic sensor 321. The same goes for the time when the magnet 314 approaches the magnetic sensor 321. Also, the same goes for the magnetic sensors 322 and 323.
However, there is a case where the magnetization direction of the magnetic sensor 321 is not inverted even when the magnet 311, 312, 313 or 314 approaches the magnetic sensor 321. In this case, neither the positive directional detection pulse nor the negative directional detection pulse is outputted from the magnetic sensor 321. For instance, it is assumed that the movable section 302 is rotated in the rightward direction, the magnet 311 approaches the magnetic sensor 321, the magnetization direction of the magnetic sensor 321 is inverted, the positive directional detection pulse is outputted from the magnetic sensor 321, and then, the movable section 302 changes its rotation direction from the rightward direction to the leftward direction, and the magnet 311 approaches the magnetic sensor 321 again. In such a case, at the second time of approach of the magnet 311, neither the positive directional detection pulse nor the negative directional detection pulse is outputted from the magnetic sensor 321 because inversion of the magnetization direction of the magnetic sensor 321 does not occur. The same goes for the magnetic sensors 322 and 323. Hereinafter, a phenomenon that the magnetization direction of the magnetic sensor is not inverted at the second or more time of approach of the magnet in a case where the magnet producing the magnetic field in the same direction approaches the magnetic sensor continuously multiple times is expressed as “the magnetization direction is not inverted by addition of the magnetic field in the same direction”.
In addition, the rotation detecting apparatus 300 comprises a rotation detecting circuit 330 for detecting the rotation direction and the rotation amount of the movable section 302 on the basis of the detection pulse outputted from each of the magnetic sensors 321, 322 and 323. The rotation detecting circuit 330 receives the positive directional detection pulses and the negative directional detection pulses respectively outputted from the magnetic sensors 321, 322 and 323. The rotation detecting circuit 330 assigns numbers to the positive directional detection pulses and the negative directional detection pulses respectively outputted from the magnetic sensors 321, 322 and 323. Concretely, “1” is assigned to the positive directional detection pulse outputted from the magnetic sensor 321, “2” is assigned to the positive directional detection pulse outputted from the magnetic sensor 322, and “3” is assigned to the positive directional detection pulse outputted from the magnetic sensor 323. Moreover, “4” is assigned to the negative directional detection pulse outputted from the magnetic sensor 321, “5” is assigned to the negative directional detection pulse outputted from the magnetic sensor 322, and “6” is assigned to the negative directional detection pulse outputted from the magnetic sensor 323. The rotation detecting circuit 330 carries out operation processing using the number assigned to each detection pulse to decide the rotation direction and the rotation amount of the movable section 302.
(Four Kinds of Normal Processes)
Hereinafter, four kinds of normal processes carried out by the rotation detecting circuit 330 in order to decide the rotation direction and the rotation amount of the movable section 302 will be explained.
Firstly, a first normal process is a process of deciding the rotation amount of the movable section 302 in a case where the movable section 302 is rotated in the rightward direction. The first normal process is as follows. For instance, the movable section 302 is rotated in the rightward direction by approximately 180 degrees. In the meantime, the magnet 311 approaches the magnetic sensors 321, 322 and 323 sequentially, and the magnetization directions of the magnetic sensors 321, 322 and 323 are inverted sequentially, and then, the magnet 312 approaches the magnetic sensors 321, 322 and 323 sequentially, and the magnetization directions of the magnetic sensors 321, 322 and 323 are inverted sequentially. In this case, an order of the numbers of the detection pulses outputted from the magnetic sensors 321, 322 and 323 becomes “1”, “2”, “3”, “4”, “5”, “6”. Thus, in the case where the movable section 302 is rotated in the rightward direction, the number of the outputted detection pulse is repeated in the order of “1”, “2”, “3”, “4”, “5”, “6”. On the basis of such regularity, the rotation detecting circuit 330 performs the following process as the first normal process. Namely, the rotation detecting circuit 330 increases the rotation amount by 1 in a case where a difference between the number of the detection pulse outputted from any one of the magnetic sensors 321, 322 and 323 last time and the number of the detection pulse outputted from any one of the magnetic sensors 321, 322 and 323 at the present time is 1 and the rotation direction when the detection pulse is outputted last time is the rightward direction. Incidentally, in a case where the number of the detection pulse outputted last time is “6” and the number of the detection pulse outputted at the present time is “1”, the rotation detecting circuit 330 calculates the difference between both the numbers by 1 on the basis of the above-mentioned regularity. Incidentally, the first normal process is explained in detail in paragraphs 0127 to 0141, FIG. 7 and an upper stage of FIG. 8 of Patent Document 1.
Next, a second normal process is a process of deciding the rotation amount of the movable section 302 in a case where the movable section 302 is rotated in the leftward direction. The second normal process is as follows. For instance, the movable section 302 is rotated in the leftward direction by approximately 180 degrees. In the meantime, the magnet 314 approaches the magnetic sensors 323, 322 and 321 sequentially, and the magnetization directions of the magnetic sensors 323, 322 and 321 are inverted sequentially, and then, the magnet 313 approaches the magnetic sensors 323, 322 and 321 sequentially, and the magnetization directions of the magnetic sensors 323, 322 and 321 are inverted sequentially. In this case, an order of the numbers of the detection pulses outputted from the magnetic sensors 321, 322 and 323 becomes “6”, “5”, “4”, “3”, “2”, “1”. Thus, in the case where the movable section 302 is rotated in the leftward direction, the number of the outputted detection pulse is repeated in the order of “6”, “5”, “4”, “3”, “2”, “1”. On the basis of such regularity, the rotation detecting circuit 330 performs the following process as the second normal process. Namely, the rotation detecting circuit 330 decreases the rotation amount by 1 in a case where a difference between the number of the detection pulse outputted from any one of the magnetic sensors 321, 322 and 323 last time and the number of the detection pulse outputted from any one of the magnetic sensors 321, 322 and 323 at the present time is 1 and the rotation direction when the detection pulse is outputted last time is the leftward direction. Incidentally, in a case where the number of the detection pulse outputted last time is “1” and the number of the detection pulse outputted at the present time is “6”, the rotation detecting circuit 330 calculates the difference between both the numbers by 1 on the basis of the above-mentioned regularity.
Next, a third normal process is a process of deciding the rotation direction and the rotation amount of the movable section 302 in a case where the movable section 302 changes the rotation direction from the rightward direction to the leftward direction. The third normal process is as follows. For instance, it is assumed that the movable section 302 is rotated in the rightward direction by approximately 90 degrees, in the meantime, the magnet 311 approaches the magnetic sensors 321, 322 and 323 sequentially and the magnetization directions of the magnetic sensors 321, 322 and 323 are inverted sequentially. It is assumed that, after that, the movable section 302 changes the rotation direction to the leftward direction and is rotated in the leftward direction by approximately 180 degrees, in the meantime, the magnet 311 approaches the magnetic sensors 323, 322 and 321 sequentially, but, in all of the magnetic sensors 321, 322 and 323, the magnetization direction is not inverted by addition of the magnetic field in the same direction, and subsequently, the magnet 314 approaches the magnetic sensors 323, 322 and 321 sequentially and the magnetization directions of the magnetic sensors 323, 322 and 321 are inverted sequentially. In this case, an order of the numbers of the detection pulses outputted from the magnetic sensors 321, 322 and 323 becomes “1”, “2”, “3”, “6”, “5”, “4”. A point to be noted here is that the number of detection pulse outputted at last before the rotation direction of the movable section 302 is changed is “3”, the number of detection pulse outputted at first after the rotation direction of the movable section 302 is changed is “6”, and the difference between these numbers is 3. Thus, if the movable section 302 changes the rotation direction, the difference between the numbers of the detection pulses before and after change of the rotation direction becomes 3. On the basis of such regularity, the rotation detecting circuit 330 performs the following process as the third normal process. Namely, the rotation detecting circuit 330 decides that the rotation direction of the movable section 302 is changed from the rightward direction to the leftward direction and decreases the rotation amount by 3 in a case where a difference between the number of the detection pulse outputted from any one of the magnetic sensors 321, 322 and 323 last time and the number of the detection pulse outputted from any one of the magnetic sensors 321, 322 and 323 at the present time is 3 and the rotation direction when the detection pulse is outputted last time is the rightward direction. Incidentally, the third normal process is explained in detail in paragraphs 0157 to 0168, FIG. 7 and an upper stage of FIG. 9 of Patent Document 1.
Finally, a fourth normal process is a process of deciding the rotation direction and the rotation amount of the movable section 302 in a case where the movable section 302 changes the rotation direction from the leftward direction to the rightward direction. The fourth normal process is the process carried out, for instance, in a case where the movable section 302 is rotated in the leftward direction by approximately 90 degrees, and then, changes the rotation direction to the rightward direction and is rotated in the rightward direction by approximately 180 degrees. That is, although the above-mentioned third normal process is the process carried out when the movable section 302 changes the rotation direction from the rightward direction to the leftward direction, the fourth normal process is the process carried out when the movable section 302 changes the rotation direction from the leftward direction to the rightward direction. As the fourth normal process, the rotation detecting circuit 330 decides that the rotation direction of the movable section 302 is changed from the leftward direction to the rightward direction and increases the rotation amount by 3, in a case where a difference between the number of the detection pulse outputted from any one of the magnetic sensors 321, 322 and 323 last time and the number of the detection pulse outputted from any one of the magnetic sensors 321, 322 and 323 at the present time is 3 and the rotation direction when the detection pulse is outputted last time is the leftward direction.
Incidentally, when the movable section 302 is rotated at first after the rotation detecting apparatus 300 starts operation, the rotation direction of the movable section 302 is decided, for instance, on the basis of whether a value obtained by subtracting the number of the detection pulse outputted from the magnetic sensor 321 from the number of the detection pulse outputted from the magnetic sensor 322 is positive or negative, and its result is stored as rotation direction information in a storage element provided in the rotation detecting circuit 330. Afterwards, whenever change of the rotation direction of the movable section 302 is recognized by the above-mentioned processes, the rotation direction information stored in the storage element is updated. The rotation detecting circuit 330 can know the rotation direction at the time when the detection pulse is outputted last time by reading the rotation direction information from the storage element.
(Missing of Detection Pulse)
The above-mentioned four normal processes in the rotation detecting circuit 330 are processes on the assumption that, when the magnetization direction of any one of the magnetic sensors 321, 322 and 323 is inverted, the detection pulse is invariably outputted from that magnetic sensor. However, in each of the magnetic sensors 321, 322 and 323, a situation that the detection pulse is not outputted regardless of inversion of the magnetization direction, i.e., missing of the detection pulse may be caused. In a case where the missing of the detection pulse occurs, it is impossible to correctly detect the rotation direction and the rotation amount of the movable section 302 in the above-mentioned normal processes.
Hereinafter, a situation that correct decision of the rotation direction and the rotation amount of the movable section 302 in the above-mentioned normal processes becomes impossible in the case where missing of the detection pulse occurs will be explained by using two operation examples of the rotation detecting apparatus 300.
Firstly, a first operation example is as follows. For instance, it is assumed that the movable section 302 is rotated in the rightward direction by approximately 150 degrees, in the meantime, the magnet 311 approaches the magnetic sensors 321, 322 and 323 sequentially, and the magnetization directions of the magnetic sensors 321, 322 and 323 are inverted sequentially, and then, the magnet 312 approaches the magnetic sensors 321 and 322 sequentially, and the magnetization directions of the magnetic sensors 321 and 322 are inverted sequentially. In this case, an order of the numbers of the detection pulses outputted from the magnetic sensors 321, 322 and 323 becomes “1”, “2”, “3”, “4”, “5”. In this operation, it is assumed that the negative directional detection pulse (the number “4”) to be outputted from the magnetic sensor 321 is missed. In this case, the order of the numbers of the detection pulses becomes “1”, “2”, “3”, “5”.
Next, a second operation example is as follows. For instance, it is assumed that the movable section 302 is rotated in the rightward direction by approximately 90 degrees, in the meantime, the magnet 311 approaches the magnetic sensors 321, 322 and 323 sequentially, and the magnetization directions of the magnetic sensors 321, 322 and 323 are inverted sequentially. Subsequently, it is assumed that the movable section 302 changes the rotation direction to the leftward direction, is rotated in the leftward direction by approximately 150 degrees, in the meantime, the magnet 311 approaches the magnetic sensors 323, 322 and 321 sequentially, but the magnetization directions of the magnetic sensors 321, 322 and 323 are not inverted by addition of the magnetic field in the same direction, and further, the magnet 314 approaches the magnetic sensors 323 and 322 sequentially, and the magnetization directions of the magnetic sensors 323 and 322 are inverted sequentially. In this case, an order of the numbers of the detection pulses outputted from the magnetic sensors 321, 322 and 323 becomes “1”, “2”, “3”, “6”, “5”. In this operation, it is assumed that the negative directional detection pulse (the number “6”) to be outputted from the magnetic sensor 323 is missed. In this case, the order of the numbers of the detection pulses becomes “1”, “2”, “3”, “5”.
By comparing the case where the negative directional detection pulse of the magnetic sensor 321 is missed in the first operation example to the case where the negative directional detection pulse of the magnetic sensor 323 is missed in the second operation example, it is understandable that the orders of the numbers of the detection pulses are the same. In this case, it is impossible to identify these two operations in the above-mentioned normal processes, and consequently, it is impossible to correctly decide the rotation direction and the rotation amount of the movable section 302.
(Missing Complementing Process)
The rotation detecting circuit 330 includes the function of carrying out processes (hereinafter, this is called as “missing complementing process”) for complementing such missing of the detection pulse and correctly deciding the rotation direction and the rotation amount of the movable section 302. Hereinafter, three examples of the missing complementing process will be explained.
Firstly, a first example of the missing complementing process is an example of the missing complementing process in a case where the movable section 302 does not change the rotation direction. The first example of the missing complementing process is as follows. For instance, it is assumed that the movable section 302 is rotated in the rightward direction by approximately 180 degrees, in the meantime, the magnet 311 approaches the magnetic sensors 321, 322 and 323 sequentially, and the magnetization directions of the magnetic sensors 321, 322 and 323 are inverted sequentially, and then, the magnet 312 approaches the magnetic sensors 321, 322 and 323 sequentially, and the magnetization directions of the magnetic sensors 321, 322 and 323 are inverted sequentially. In this case, an order of the numbers of the detection pulses outputted from the magnetic sensors 321, 322 and 323 becomes “1”, “2”, “3”, “4”, “5”, “6”. In this operation, if the negative directional detection pulse (the number “4”) to be outputted from the magnetic sensor 321 is missed, the order of the numbers of the detection pulses becomes “1”, “2”, “3”, “5”, “6”.
In this case, the rotation detecting circuit 330 carries out the above-mentioned first normal process from the time when the detection pulse of the number “1” is outputted to the time when the detection pulse of the number “3” is outputted to increase the rotation amount of the movable section 302 by 1 for every time when the detection pulse is outputted. Subsequently, at the time when the detection pulse of the number “5” is outputted, the rotation detecting circuit 330 recognizes that missing of the detection pulse occurs during the time until the detection pulse of the number “5” is outputted after the detection pulse of the number “3” is outputted because a difference between the number “5” of the present detection pulse and the number “3” of the detection pulse outputted immediately before the present detection pulse is 2 and the difference is neither 1 nor 3. Further, at the time when the detection pulse of the number “5” is outputted, the rotation detecting circuit 330 does not change the rotation amount of the movable section 302. Next, at the time when the detection pulse of the number “6” is outputted, the rotation detecting circuit 330 subtracts the number “5” of the detection pulse outputted immediately before the present detection pulse from the number “6” of the present detection pulse and thereby obtains a value of 1, and therefore, decides that the rotation direction of the movable section 302 at the time when the detection pulse of the number “6” is outputted is the rightward direction. Further, at the time when the detection pulse of the number “6” is outputted, the rotation detecting circuit 330 subtracts the number “3” of the detection pulse (the detection pulse before last) outputted two times before the present detection pulse from the number “6” of the present detection pulse, and changes the rotation amount of the movable section 302 on the basis of a value obtained by this subtraction and the rotation direction of the movable section 302 at the time when the detection pulse of the number “6” is outputted.
Namely, in a case where the rotation direction of the movable section 302 is the rightward direction at the time when the decision of the rotation direction and the rotation amount is carried out (in this example, at the time when the detection pulse of the number “6” is outputted) and a case where a value obtained by subtracting the number of the detection pulse outputted two times before the present detection pulse from the present detection pulse outputted at the time when the decision of the rotation direction and the rotation amount is carried out is g (a positive value), the rotation amount of the movable section 302 is increased by g. Moreover, in the case where the rotation direction of the movable section 302 is the rightward direction at the time when the decision of the rotation direction and the rotation amount is carried out and a case where a value obtained by subtracting the number of the detection pulse outputted two times before the present detection pulse from the present detection pulse outputted at the time when the decision of the rotation direction and the rotation amount is carried out is −h (a negative value), the rotation amount of the movable section 302 is increased by (6−h) (6 used here is the number of kinds of the detection pulses). In this example, because the rotation direction of the movable section 302 is the rightward direction at the time when the decision of the rotation direction and the rotation amount is carried out, i.e., at the time when the detection pulse of the number “6” is outputted, and a value obtained by subtracting the number of the detection pulse outputted two times before the present detection pulse from the present detection pulse outputted at the time when the detection pulse of the number “6” is outputted is 3, the rotation detecting circuit 330 increases the rotation amount of the movable section 302 by 3. As mentioned above, if there is no missing of the negative directional detection pulse in the magnetic sensor 321, the order of the detection pulses becomes “1”, “2”, “3”, “4”, “5”, “6” and the rotation amount of the movable section 302 rotated in the rightward direction during the time until the detection pulse of the number “6” is outputted after the detection pulse of the number “3” is outputted is increased by 3. From this, it is understandable that decision obtained by the missing complementing process of increasing the rotation amount of the movable section 302 by 3 is correct. Incidentally, the first example of the missing complementing process is explained in detail in paragraphs 0142 to 0156, FIG. 7 and a lower stage of FIG. 8 of Patent Document 1.
Next, a second example of the missing complementing process is an example of the missing complementing process in a case where the movable section 302 changes the rotation direction once. The second example of the missing complementing process is as follows. For instance, it is assumed that the movable section 302 is rotated in the rightward direction by approximately 90 degrees, in the meantime, the magnet 311 approaches the magnetic sensors 321, 322 and 323 sequentially, and the magnetization directions of the magnetic sensors 321, 322 and 323 are inverted sequentially. Subsequently, it is assumed that the movable section 302 changes the rotation direction to the leftward direction, is rotated in the leftward direction by approximately 180 degrees, in the meantime, the magnet 311 approaches the magnetic sensors 323, 322 and 321 sequentially, but the magnetization directions of the magnetic sensors 321, 322 and 323 are not inverted by addition of the magnetic field in the same direction, and further, the magnet 314 approaches the magnetic sensors 323, 322 and 321 sequentially, and the magnetization directions of the magnetic sensors 323, 322 and 321 are inverted sequentially. In this case, an order of the numbers of the detection pulses outputted from the magnetic sensors 321, 322 and 323 becomes “1”, “2”, “3”, “6”, “5”, “4”. In this operation, if the negative directional detection pulse (the number “6”) to be outputted from the magnetic sensor 323 is missed, the order of the numbers of the detection pulses becomes “1”, “2”, “3”, “5”, “4”.
In this case, the rotation detecting circuit 330 carries out the above-mentioned first normal process from the time when the detection pulse of the number “1” is outputted to the time when the detection pulse of the number “3” is outputted to increase the rotation amount of the movable section 302 by 1 for every time when the detection pulse is outputted. Subsequently, at the time when the detection pulse of the number “5” is outputted, the rotation detecting circuit 330 recognizes that missing of the detection pulse occurs during the time until the detection pulse of the number “5” is outputted after the detection pulse of the number “3” is outputted because a difference between the number “5” of the present detection pulse and the number “3” of the detection pulse outputted immediately before the present detection pulse is 2 and the difference is neither 1 nor 3. Further, at the time when the detection pulse of the number “5” is outputted, the rotation detecting circuit 330 does not change the rotation amount of the movable section 302. Next, at the time when the detection pulse of the number “4” is outputted, the rotation detecting circuit 330 subtracts the number “5” of the detection pulse outputted immediately before the present detection pulse from the number “4” of the present detection pulse and thereby obtains a value of −1, and therefore, decides that the rotation direction of the movable section 302 at the time when the detection pulse of the number “4” is outputted is the leftward direction. Further, at the time when the detection pulse of the number “4” is outputted, the rotation detecting circuit 330 subtracts the number “3” of the detection pulse (the detection pulse before last) outputted two times before the present detection pulse from the number “4” of the present detection pulse, and changes the rotation amount of the movable section 302 on the basis of a value obtained by this subtraction and the rotation direction of the movable section 302 at the time when the detection pulse of the number “4” is outputted.
Namely, in a case where the rotation direction of the movable section 302 is the leftward direction at the time when the decision of the rotation direction and the rotation amount is carried out (in this example, at the time when the detection pulse of the number “4” is outputted) and a case where a value obtained by subtracting the number of the detection pulse outputted two times before the present detection pulse from the present detection pulse outputted at the time when the decision of the rotation direction and the rotation amount is carried out is −i (a negative value), the rotation amount of the movable section 302 is decreased by i. Moreover, in the case where the rotation direction of the movable section 302 is the leftward direction at the time when the decision of the rotation direction and the rotation amount is carried out and a case where a value obtained by subtracting the number of the detection pulse outputted two times before the present detection pulse from the present detection pulse outputted at the time when the decision of the rotation direction and the rotation amount is carried out is j (a positive value), the rotation amount of the movable section 302 is decreased by (6−j) (6 used here is the number of kinds of the detection pulses). In this example, because the rotation direction of the movable section 302 is the leftward direction at the time when the decision of the rotation direction and the rotation amount is carried out, i.e., at the time when the detection pulse of the number “4” is outputted, and a value obtained by subtracting the number of the detection pulse outputted two times before the present detection pulse from the present detection pulse outputted at the time when the detection pulse of the number “4” is outputted is 1, the rotation detecting circuit 330 decreases the rotation amount of the movable section 302 by 5. As mentioned above, if there is no missing of the negative directional detection pulse in the magnetic sensor 323, the order of the detection pulses becomes “1”, “2”, “3”, “6”, “5”, “4” and the rotation amount of the movable section 302 rotated in the leftward direction during the time until the detection pulse of the number “4” is outputted after the detection pulse of the number “3” is outputted is decreased by 5. From this, it is understandable that decision obtained by the missing complementing process of decreasing the rotation amount of the movable section 302 by 5 is correct. Incidentally, the second example of the missing complementing process is explained in detail in paragraphs 0169 to 0184, FIG. 7 and a lower stage of FIG. 9 of Patent Document 1.
Finally, a third example of the missing complementing process is an example of the missing complementing process in a case where the movable section 302 changes the rotation direction twice. The third example of the missing complementing process is as follows. For instance, it is assumed that the movable section 302 is rotated in the rightward direction by approximately 90 degrees, in the meantime, the magnet 311 approaches the magnetic sensors 321, 322 and 323 sequentially, and the magnetization directions of the magnetic sensors 321, 322 and 323 are inverted sequentially. Subsequently, it is assumed that the movable section 302 changes the rotation direction to the leftward direction, is rotated in the leftward direction by approximately 120 degrees, in the meantime, the magnet 311 approaches the magnetic sensors 323, 322 and 321 sequentially, but the magnetization directions of the magnetic sensors 321, 322 and 323 are not inverted by addition of the magnetic field in the same direction, and further, the magnet 314 approaches the magnetic sensor 323 and the magnetization direction of the magnetic sensor 323 is inverted. Subsequently, it is assumed that the movable section 302 changes the rotation direction to the rightward direction, is rotated in the rightward direction by approximately 150 degrees, in the meantime, the magnet 314 approaches the magnetic sensor 323, but the magnetization direction of the magnetic sensor 323 is not inverted by addition of the magnetic field in the same direction, and further, the magnet 311 approaches the magnetic sensors 321 and 322 sequentially, but the magnetization directions of the magnetic sensors 321 and 322 are not inverted by addition of the magnetic field in the same direction, and furthermore, the magnet 311 approaches the magnetic sensor 323, and the magnetization direction of the magnetic sensor 323 is inverted, and moreover, the magnet 312 approaches the magnetic sensor 321, and the magnetization direction of the magnetic sensor 321 is inverted. In this case, an order of the numbers of the detection pulses outputted from the magnetic sensors 321, 322 and 323 becomes “1”, “2”, “3”, “6”, “3”, “4”. In this operation, if the positive directional detection pulse (the number “3”) to be outputted from the magnetic sensor 323 at first time is missed, the order of the numbers of the detection pulses becomes “1”, “2”, “6”, “3”, “4”.
In this case, the rotation detecting circuit 330 carries out the above-mentioned first normal process from the time when the detection pulse of the number “1” is outputted to the time when the detection pulse of the number “2” is outputted to increase the rotation amount of the movable section 302 by 1 for every time when the detection pulse is outputted. Subsequently, at the time when the detection pulse of the number “6” is outputted, the rotation detecting circuit 330 recognizes that missing of the detection pulse occurs during the time until the detection pulse of the number “6” is outputted after the detection pulse of the number “2” is outputted because a difference between the number “6” of the present detection pulse and the number “2” of the detection pulse outputted immediately before the present detection pulse is 4 and the difference is neither 1 nor 3. Further, at the time when the detection pulse of the number “6” is outputted, the rotation detecting circuit 330 does not change the rotation amount of the movable section 302. Next, at the time when the detection pulse of the number “3” is outputted, the rotation detecting circuit 330 subtracts the number “6” of the detection pulse outputted immediately before the present detection pulse from the number “3” of the present detection pulse and obtains a value of neither 1 nor −1, and subsequently, the rotation detecting circuit 330 subtracts the number “2” of the detection pulse outputted two times before the present detection pulse from the number “3” of the present detection pulse and obtains a value of 1, and therefore, decides that the rotation direction of the movable section 302 at the time when the detection pulse of the number “3” is outputted is the rightward direction (about this deciding step, refer to steps S7 and S9 in FIG. 7 of Patent Document 1). Further, at the time when the detection pulse of the number “3” is outputted, the rotation detecting circuit 330 subtracts the number “2” of the detection pulse outputted two times before the present detection pulse from the number “3” of the present detection pulse, and changes the rotation amount of the movable section 302 on the basis of a value obtained by this subtraction and the rotation direction of the movable section 302 at the time when the detection pulse of the number “3” is outputted. Namely, because the rotation direction of the movable section 302 is the rightward direction at the time when the detection pulse of the number “3” is outputted and a value obtained by subtracting the number of the detection pulse outputted two times before the present detection pulse from the present detection pulse outputted at the time when the detection pulse of the number “3” is outputted is 1, the rotation detecting circuit 330 increases the rotation amount of the movable section 302 by 1. As mentioned above, if there is no missing of the positive directional detection pulse in the magnetic sensor 323, the order of the detection pulses becomes “1”, “2”, “3”, “6”, “3”, “4” and the rotation amount of the movable section 302 rotated in the leftward direction and then rotated in the rightward direction during the time until the detection pulse of the number “3” is outputted at second time after the detection pulse of the number “2” is outputted is increased by 1. From this, it is understandable that decision obtained by the missing complementing process of decreasing the rotation amount of the movable section 302 by 1 is correct. Incidentally, the third example of the missing complementing process is explained in detail in paragraphs 0197 to 0212, FIG. 7 and a lower stage of FIG. 10 of Patent Document 1.
By such missing complementing processes, it is possible to improve detection accuracy of the rotation direction and the rotation amount of the rotation shaft 301 (the movable section 302). More detail contents of the rotation detecting apparatus 300 according to conventional technique is described in Patent Document 1.